Light emitting element

ABSTRACT

A light emitting element includes a semiconductor layer; an upper electrode disposed on an upper surface of the semiconductor layer; and a lower electrode disposed on a lower surface of the semiconductor later. In a plan view, the upper electrode includes a first extending portion extending in an approximately rectangular shape along an outer periphery of the semiconductor layer, a first pad portion connected to a first side among four sides of the first extending portion, a second pad portion connected to a second side that is opposite to the first side, among the four sides of the first extending portion, and a second extending portion and a third extending portion, each disposed in a region surrounded by the first extending portion, the second extending portion and the third extending portion each connecting the first pad portion and the second pad portion.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/869,667, filed on Sep. 29, 2015, now U.S. Pat. No. 9,553,237, whichclaims priority to Japanese Patent Application No. 2014-201511, filed onSep. 30, 2014, the entire disclosures of which are hereby incorporatedherein by reference.

BACKGROUND

1. Technical Field

The present disclosure relates to a light emitting element that includesa semiconductor layer, an upper electrode disposed on an upper surfaceof the semiconductor layer, and a lower electrode disposed on a lowersurface of the semiconductor layer.

2. Background Art

There have been light emitting elements in which a “pad” is disposed onat each of two adjacent corners of an approximately rectangular uppersurface of a semiconductor layer, and a “fine wire electrode” isdisposed in a grid shape extending from the pad electrode, as describedin JP2013-197197A.

However, with such a conventional structure, uneven emission tends tooccur. Generally, a higher current density occurs in a region close tothe pad to which the wire for supplying current from an external powersource is connected, and even with a fine wire electrode, the currentdensity decreases as the distance from the pad increases. As a result,stronger emission occurs near the pad, which tends to result in unevenbrightness in the emission of the light emitting element as a whole.

Certain embodiments of the present invention have been devised in viewof such circumstances, and an object thereof is to provide a lightemitting element that can emit light more uniformly.

According to certain embodiments of the present invention, a lightemitting element includes a semiconductor layer, an upper electrodedisposed on an upper surface of the semiconductor layer, and a lowerelectrode disposed on a lower surface of the semiconductor layer. Thelight emitting element has an approximately rectangular shape in a planview. In the plan view, the upper electrode includes a first extendingportion extending in an approximately rectangular shape with four sides,along outer periphery of the semiconductor layer, a first pad portionconnected to a first side among the four sides of the first extendingportion, a second pad portion connected to a second side which isopposite to the first side, and a second extending portion and a thirdextending portion each disposed in a region surrounded by the firstextending portion and respectively connecting the first pad portion andthe second pad portion. With respect to a first straight line connectingthe first pad portion and the second pad portion with a shortestdistance, the second extending portion is disposed in a region closer tothe third side of the four sides, and the third extending portion isdisposed in a region closer to the forth side which is opposite to thethird side. On a second straight line perpendicularly bisecting thefirst straight line, a distance between the second extending portion andthe third extending portion is equal to or greater than a shortestdistance between the first extending portion and the second extendingportion, and equal to or greater than a shortest distance between thefirst extending portion and the third extending portion.

According to certain embodiments of the present invention, it ispossible to obtain a light emitting element in which uneven currentdensity on the upper surface of the semiconductor layer can be reduced,which allows for more uniform emission.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic plan view, seen from an upper electrode side, of alight emitting element according to a first embodiment.

FIG. 2 is a schematic cross sectional view taken along line L1 of FIG.1.

FIG. 3 is a schematic cross sectional view taken along line L2 of FIG.1.

FIG. 4 is a diagram illustrating an emission intensity distribution ofthe light emitting element according to the first embodiment.

FIG. 5 is a schematic plan view, seen from an upper electrode side, of alight emitting element according to a second embodiment.

FIG. 6 is a schematic plan view, seen from an upper electrode side, of alight emitting element according to a third embodiment.

FIG. 7 is a diagram illustrating an emission intensity distribution ofthe light emitting element according to Comparative Example 1.

FIG. 8 is a diagram illustrating an emission intensity distribution ofthe light emitting element according to Comparative Example 2.

DETAILED DESCRIPTION

A light emitting element according to embodiments the present inventionwill be described below with reference to the accompanying drawings. Theembodiments shown below are intended as illustrative to give concreteform to technical ideas of the present invention, and the scope of theinvention is not limited to those described below. Further, in thedescription below, the same designations or the same reference numeralsdenote the same or like members and duplicative descriptions will beappropriately omitted.

First Embodiment

FIG. 1 is a schematic plan view, seen from an upper electrode side, of alight emitting element 100 according to a first embodiment. FIG. 2 is aschematic cross sectional view taken along line L1 of FIG. 1A, and FIG.3 is a schematic cross sectional view taken along line L2 of FIG. 1.FIG. 4 is a diagram illustrating an emission intensity distribution ofthe light emitting element 100 according to the first embodiment, at aninjection current of 500 mA.

As shown in FIGS. 1 to 4, the light emitting element 100 according tothe first embodiment includes a semiconductor layer 10, an upperelectrode disposed on an upper surface 12 of the semiconductor layer 10,and a lower electrode 50 disposed on a lower surface of thesemiconductor layer 10, and has an approximately rectangular shape in aplan view. In a plan view, the upper electrode includes a firstextending portion 20 extending in an approximately rectangular shapewith four sides along an outer periphery of the semiconductor layer 10,a first pad portion 26 connected to a first side among the four sides ofthe first extending portion 20, a second pad portion 28 connected to asecond side 20 b which is opposite to the first side 20 a, and a secondextending portion 22 and a third extending portion 24, each disposed ina region surrounded by the first extending portion 20 and respectivelyconnecting the first pad portion 26 and the second pad portion 28. Withrespect to a first straight line L1 connecting the first pad portion 26and the second pad portion 28 with a shortest distance, the secondextending portion 22 is disposed in a region closer to the third side 20c of the four sides, and the third extending portion 24 is disposed in aregion closer to the forth side 20 d opposite to the third side 20 c. Ona second straight line L2 perpendicularly bisecting the first straightline L1, a distance X2 between the second extending portion 22 and thethird extending portion 24 is equal or greater than a shortest distanceX1 between the first extending portion 20 and the second extendingportion 22, and equal or greater than a shortest distance X3 between thefirst extending portion 20 and the third extending portion 24.

With this arrangement, uneven current density on the upper surface 12 ofthe semiconductor layer 10 can be reduced and more uniform emission canbe obtained.

Generally, an electrically conductive member such as a wire is connectedto the pad portion to inject current to the light emitting element. As aresult, a higher current density occurs in a region close to the padportion and the current density decreases as the distance from the padportion increases. In order to compensate for uneven current density, anextending portion extending from the pad portion may be provided todiffuse the electric current in a wider region. However, even when suchan extending portion is provided, the current density decreases as thedistance from the pad portion increases. Thus, uniform emission of thelight emitting element as a whole has been difficult to obtain.

Accordingly, in the light emitting element 100, among the four sides ofthe first extending portion 20 having an approximately rectangularshape, the first pad portion 26 is disposed connected to the first side20 a and the second pad portion 28 is disposed connected to the secondside 20 b opposite the first side 20 a. Thus, excessive distribution ofcurrent density in a region closer to one of opposite sides of the firstextending portion 20 can be reduced. Further, a second extending portionand a third extending portion are respectively disposed in a regionsurrounded by the first extending portion, so as to connect the firstpad portion and the second pad portion respectively. This arrangementallows for an increase in the amount of electric current flows into thesecond extending portion 22 and the third extending portion 24 which arecloser to each pad portion 26 and 28 than to the first extending portion20. In addition, with respect to the first straight line L1 connectingthe first pad portion 26 and the second pad portion in a shortestdistance, the second extending portion 22 is arranged in a region closerto the third side 20 c, and the third extending portion 24 is arrangedin a region closer to the fourth side 20 d which is opposite to thethird side. According to this configuration, a center portion C which isspaced apart from the first pad portion 26 and the second pad portion 28and has a low electric current density can be surrounded by the secondextending portion 22 and the third extending portion 24, so that theelectric current can be concentrated from the high current densityportions around the pad electrodes 26 and 28. Further, on a secondstraight line L2 perpendicularly bisecting the first straight line L1, adistance X2 between the second extending portion 22 and the thirdextending portion 24 is equal to or greater than a shortest distance X1between the first extending portion 20 and the second extending portion22, and equal to or greater than a shortest distance X3 between thefirst extending portion 20 and the third extending portion 24. With thisconfiguration, excessively high electrical density in a regionsurrounded by the second extending portion 22 and the third extendingportion 24 can be prevented compared to a region between the third side20 c of the first extending portion 20 and the second extending portion22 (22 c), and the region between the fourth side 22 d of the firstextending portion 20 and the third extending portion 24 (24 c).Accordingly, uneven distribution of current density in the upper surface12 of the semiconductor layer 10 can be reduced and as shown in FIG. 4,more uniform light emission becomes possible to obtain. In thespecification, the term “center portion C” refers to an intersectionpoint of two straight lines which are crossing each other and equally orapproximately equally dividing the upper surface 12 of the semiconductorlayer 10 in four areas. For example, as shown in FIG. 1, in the casewhere the upper surface 12 of the semiconductor layer 10 has a squareshape, the intersection point of two diagonal lines can serve as the“center portion C”.

The main components of the light emitting element 100 will be describedbelow.

Semiconductor Layer 10

The materials and/or the structure of the semiconductor layer 10 are notspecifically limited and can be selected from various appropriatematerials and structures. In the first embodiment, a structure in whichan n-type semiconductor layer 10 a, an active layer 10 b, a p-typesemiconductor layer 10 c are stacked in this order is employed; nitridesemiconductors such as In_(X)Al_(Y)Ga_(1-X-Y)N (0=<X<1, 0=<Y<1,0=<X+Y<1) are used as the material of each layer. The nitridesemiconductors have higher internal resistance compared to that of othermaterials such as GaAs, so that efficient current spreading is difficultto obtain. Accordingly, an especially effective result can be expectedin the case of forming the semiconductor layer with nitridesemiconductors in the first embodiment.

In the first embodiment, the n-type semiconductor layer 10 a is referredto as the upper surface 12 and the p-type semiconductor layer 10 c isreferred to as the lower surface. In the light emitting element 100, theupper surface 12 serves as the light extracting surface, and the lowersurface is electrically connected to a support member 30 or the like,which will be described below. The upper surface 12 preferably has arectangular shape. Generally, individual light emitting elements aresingulated from a wafer, so that in view of manufacturing yield, theupper surface 12 preferably has a square shape or an approximatelysquare shape.

In the first embodiment, the upper surface 12 has a square shape with aside of about 1.0 mm, but the size of the upper surface 12 can beappropriately selected. In the case of the upper surface 12 having asquare shape (or an approximately square shape), a side may be 0.5 mm orgreater, preferably 0.8 mm or greater. This is because with a smallplanar dimension of the upper surface 12, the electric current densitybetween the first pad portion 26 and the second pad portion 28 will beexcessively high, which may be undesirable. The upper limit for a sideis not specifically limited, but in order not to have excessively lowelectric current density around the center portion C, a side may be 2.0mm or less, preferably 1.5 mm or less.

Upper Electrode 20, 22, 24, 26, 28

The upper electrode is provided on the upper surface 12 of thesemiconductor layer 10, and at least includes the first pad portion 26,the second pad portion 28, the first extending portion 20, the secondextending portion, and the third extending portion 24. Morespecifically, in a plan view of the light emitting element 100 seen froman upper surface 12 side, of the four sides of the rectangular shape ofthe outer periphery of the semiconductor layer 10, the first pad portion26 is disposed near one of the four sides and the second pad portion isdisposed near the side which is opposite to the one of the four sides.The first pad portion 26 and the second pad portion 28 are the portionsto which electric current is supplied from outside via conductivemembers such as wires.

The first pad portion 26 and the second pad portion 28 are connected tothe first extending portion 20 which extends in an approximatelyrectangular shape along the outer periphery of the semiconductor layer10. More specifically, in the region surrounded by the first extendingportion 20, the first pad portion 26 is connected to the first side 20 aamong the four sides of the first extending portion 10, and the secondpad portion 28 is connected to the second side 20 b that is opposite tothe first side 20 a. As described above, the first pad portion 26 andthe second pad portion 28 are connected in the regions surrounded by thefirst extending portion 20, that is, connected to inner sides than thefirst extending portion 20, so that the region surrounded by the firstextending portion 20 can be increased. Thus, this configuration ispreferable, allowing for a larger light emitting surface area of thelight emitting element 100. The first pad portion 26 and the second padportion 28 are respectively arranged on a third straight line L3 passingthrough the intersection point of the diagonal lines of the firstextending portion 20. With this arrangement, the pad portions 26 and 28are arranged substantially point symmetrical to the center portion C, sothat uneven distribution of electric current density in the regionsurrounded by the first extending portion 20 can be reduced. Further, inthis configuration, the first pad portion 26 and the second pad portion28 are arranged such that the straight line L1 connecting the first padportion 26 and the second pad portion 28 in a shortest distance isapproximately in parallel to the third side 20 c and the fourth side 20d, which are, among the four sides of the first extending portion 20,not provided with the pad portion 26 or 28. In other words, the firststraight line L1 and the third straight line L3 are overlapped with eachother. The first pad portion 26 and the second pad portion 28 have thesame shortest distance from the third side 20 c and the fourth side 20d, so that the electric current density can be prevented from beinghigher in a region closer to the third side 20 c or the fourth side 20d.

The second extending portion 22 and the third extending portion 24 aredisposed in a region surrounded by the first extending portion 20 so asto be spaced apart from each other and connected to both the first padportion 26 and the second pad portion 28 at positions spaced apart fromeach other. With this configuration, the second extending portion 22 andthe third extending portion 24 are spaced apart from each other and alsoconnected to the first pad portion 26 and the second pad portion 28respectively. Thus, a narrow region surrounded by the second extendingportion and the third extending portion 24 at the connecting portions tothe pad portions 26 and 28 (the corner portions formed by 22 a and 24 a,22 b and 24 b) can be eliminated, which allows for suppressing theelectric current density near the pad portions 26 and 28 from beingexcessively high. Particularly, it is preferable that the firstextending portion 20 and the second extending portion 22 (22 a, 22 b)are connected to the first pad portion 26 and the second pad portion 28respectively at equal intervals from adjacent extending portions, morespecifically, at intervals of 60 degrees. With this configuration,uneven distribution of electric current density near the pad portions 26and 28 can be further decreased.

The second extending portion 22 and the third extending portion 24 aredisposed at opposite sides with respect to the first straight line L1 (aregion closer to the third side 20 c and a region closer to the fourthside 20 d of the first extending portion 20), respectively, inapproximately trapezoidal shapes at each side of the first straight lineL1 in a plan view (i.e., with a base of the trapezoids being the firststraight line L1, and the remaining sides of the trapezoids being thesecond extending portion 22 and the third extending portion 24,respectively). This allows for surrounding a wide area including thecenter portion C which is spaced apart from the pad portions 26 and 28and the electric current density tends to decrease. More specifically,the second extending portion 22 is disposed closer to the third side 20c among the four sides of the first extending portion 20 with respect tothe first straight line L1. That is, the second extending portion 22 hasextending portions 22 a, 22 b extending from outer edges of the firstpad portion 26 and the second pad portion 28, respectively, that are inthe region closer to the third side 20 c, in a straight line shape andat an angle so that the extending portions 22 a and 22 b are approachingeach other and connected to respective ends of the extending portion 22c which is approximately parallel to the third side 20 c. As describedabove, the second extending portion 22 includes a portion approximatelyin parallel to the third side 20 c. More specifically, the approximatelyin parallel portion 22 c of the second extending portion 22 with alength of a half or greater than the length of the third side 20 c ispreferable, in which case more uniform electric current densitydistribution can be obtained between the first extending portion 20 andthe second extending portion 22. Meanwhile, the third extending portion24 is disposed closer to the fourth side 20 d which is closer to thethird side 20 c. More specifically, the third extending portion 24 hasextending portions 24 a, 24 b extending from outer edges of the firstpad portion 26 and the second pad portion 28, respectively, that are inthe region closer to the fourth side 20 d, in a straight line shape andat an angle so that the extending portions 24 a and 24 b are approachingeach other and connected to respective ends of the extending portion 24c which is approximately in parallel to the fourth side 20 d. Asdescribed above, the third extending portion 24 includes a portionapproximately in parallel to the fourth side 20 d. More specifically,the approximately in parallel portion 24 c of the third extendingportion 24 with a length of a half or greater than the length of thefourth side 20 d is preferable, in which more uniform electric currentdensity distribution can be obtained between the first extending portion20 and the third extending portion 24.

In the first embodiment, on the second straight line L2 perpendicularlybisecting the first straight line L1, a distance X2 between the secondextending portion 22 and the third extending portion 24 is equal to orgreater than a shortest distance X1 between the first extending portion20 and the second extending portion 22, and equal to or greater than ashortest distance X3 between the first extending portion 20 and thethird extending portion 24. With this configuration, uneven distributionof electric current density in a region between the second extendingportion 22 and the third extending portion 24 along the second straightline L2.

On the second straight line L2, the shortest distance X1 between thefirst extending portion 20 and the second extending portion 24 and theshortest distance X3 between the first extending portion 20 and thethird extending portion 24 are preferably the same or the same. Withthis configuration, the electrical density in a region surrounded by thethird side 20 c of the first extending portion 20 and the secondextending portion 22 (22 c) and a region between the fourth side 20 d ofthe first extending portion 20 and the third extending portion 24 (24 c)can be made substantially uniform. Further, it is preferable that (i)the ratio of the shortest distance X1 between the first extendingportion 20 and the second extending portion 22, the distance between thesecond extending portion 22 and the third extending portion 23, and theshortest distance between the first extending portion 20 and the thirdextending portion 24 on the straight line L2 and (ii) the ratio of theshortest distance Y1 between the first extending portion 20 and thesecond extending portion 22, the distance between the second extendingportion 22 and the third extending portion 23, and the shortest distancebetween the first extending portion 20 and the third extending portion24 on the diagonal line of the first extending portion 20, are the same.With this configuration, the state of spreading the electric current inthe direction in the diagonal direction of the first extending portion20 can be made similar to the state of spreading the electric current inthe direction along the second straight line L2. Thus, concentration ofthe electric current in the direction along the second straight line L2can be reduced and excessive reduction in the current electric currentdensity in the vicinity of the corner portions of the first extendingportion 20 can be reduced. The term “same” used in the specification isnot limited to the case where the extending portions are arranged atprecisely the same distance or at precisely the same rate. For example,a difference within ±10%, preferably within ±5%, more preferably within±2%, may be regarded as arranged at a substantially the same distance orratio and referred to as “the same”.

The structure and the material of the upper electrode is notspecifically limited and can be selected from various appropriatestructures and the materials. In the first embodiment, the upperelectrode has a stacked-layer structure of Ti/Pt/Au (Ti, Pt, Au arestacked in this order from the semiconductor layer side). The first padelectrode portion 26 and the second pad electrode portion 28 have anappropriate circular shape with a diameter of about 100 μm. The sizes ofthe pad portions 26, 28 can be determined according to the amount of theelectric current supplied to the light emitting element 100 and the sizeof the upper surface 12 of the semiconductor layer 10. Also, the widthsof the first extending portion 20, the second extending portion 22, andthe third extending portion 24 are about 15 μm, which can be adjustedaccording to the amount of injecting current or the like. Thethicknesses of the first extending portion 20, the second extendingportion 22, and the third extending portion 24 are also not to belimited, but for example, in view of electrically conducting property,about 1 μm to about 5 μm is preferable and about 1 μm to about 3 μm ismore preferable.

Lower Electrode 50

The lower electrode 50 is an electrode disposed on a lower surface ofthe semiconductor layer 10. The lower electrode 50 is preferablydisposed at a position so as not to overlap the upper electrode whenseen through the upper surface 12 side of the semiconductor layer 10.This is because as described above, shifting the positions of the upperelectrode and the lower electrode 50 so as not to overlap each otherallows for the electric current separately flowing in the semiconductorlayer 10, which can further reduce the uneven distribution of electriccurrent density. Accordingly, an insulating film 60 such as SiO₂ ispreferably provided in a region on the lower surface of thesemiconductor layer 10 where the lower electrode 50 is not provided.This is because the bonding layer 70 which will be described below canbe prevented from being connected to the lower surface of thesemiconductor layer 10 at The support member is not limited and a knownsupport member can be used. For example, in the first embodiment, thelower electrode 50 has a stacked-layer structure of Ag/Ni/Ti/Pt, in thisorder from the semiconductor layer 10 side.

Supporting Member 30

The supporting member 30 is not an essential component, but the lightemitting element 100 includes the supporting member 30 to support thesemiconductor layer 10, and the supporting member 30 is electricallyconnected to the lower electrode 50 through the bonding layer 70 whichwill be described below. The materials and/or the structure of thesupporting member 30 are not specifically limited and can be selectedfrom various appropriate materials and structures. For example, in thefirst embodiment, Si is used as the material of the supporting member30, and in view of bonding property at the time of mounting the lightemitting element 100, a metal layer 80 which contains Au or the like ispreferably provided on the entire lower surface of the supporting member30.

Bonding Layer 70

The bonding layer 70 is an electrically conductive member for bondingthe supporting member 30 to the lower electrode 50 and the insulatingfilm 60. The materials and/or the structure of the bonding layer 70 arenot specifically limited and can be selected from various appropriatematerials and structures. For example, in the first embodiment, thebonding layer 70 has a stacked-layer structure of Ti/Pt/Au/Pt/Ti, inthis order from the semiconductor layer 10 side.

Protective Film 40

The protective film 40 is a member for protecting the semiconductorlayer 10 from physical damages caused by short circuit or by adhesion ofdust or the like. The protective film 40 defines openings in conformityto the upper surfaces of the pad portions 26, 28 for providing regionsfor connecting wires or the like, and is disposed to cover the uppersurface 12 and the side surfaces of the semiconductor layer 10. Thematerials and/or the structure of the protecting film 40 are notspecifically limited and can be selected from various appropriatematerials and structures, and for example, SiO₂ is used in the presentembodiment.

Second Embodiment

FIG. 5 is a schematic plan view, seen from an upper electrode side, of alight emitting element 200 according to a second embodiment. Next, theconfigurations different from those in the first embodiment will bedescribed.

The light emitting element 200 according to the second embodimentdiffers from the light emitting element 100 in that the second extendingportion 22 and the third extending portion 24 are arranged at oppositeside of the first straight line L1 (in the region closer to the thirdside 20 c and the region adjacent to the fourth side 20 d of the firstextending portion 20, respectively), each in a curved shape.

Accordingly, the area of the second extending portion 22 and the thirdextending portion 24 on the area of the upper surface 12 of thesemiconductor layer 10 can be reduced and thus the light extractionefficiency can be enhanced. Further, bending portions can be eliminatedfrom the second extending portion 22 and the third extending portion 24,so that the distribution of electric current density near the secondextending portion 22 and the third extending portion 24 can be made moreuniform.

Third Embodiment

FIG. 6 is a schematic plan view, seen from an upper electrode side, of alight emitting element according to a third embodiment. Next, a lightemitting device according to the second embodiment will be described.

The light emitting element 300 according to the third embodiment differsfrom the light emitting element 100 in that the first straight line L1connecting the first pad portion 26 and the second pad portion 28 in ashortest distance is arranged passing through the intersection point ofthe diagonal lines of the first extending portion 20 and at an angle tothe third side 20 c and the fourth side 20 d which are among the foursides of the first extending portion 20 and are not provided with thepad portion 26 or 28. The second extending portion 22 and the thirdextending portion 24 each connecting the pad portions 26 and 28 arearranged symmetrically with respect to the inclined first straight lineL1.

This configuration allows for a longer distance between the pad portions26 and 28, which can increase the region surrounded by the firstextending portion 20, so that the region with a low electric currentdensity can be reduced.

EXAMPLES

Effects of the light emitting element according to certain embodimentsof the present invention will be described below with reference to FIG.4 (Example 1), FIG. 7 (Comparative Example 1), and FIG. 8 (ComparativeExample 2), which have different arrangements of the upper electrodes.FIG. 4, FIG. 7, and FIG. 8 show the light emission intensity measuredfrom the upper surface (the light extracting surface) side of thesemiconductor layer at an injection current of 500 mA.

Example 1

The light emitting element according to Example 1 has an electrode shapesimilar to that of the light emitting element 100 according to the firstembodiment, and as shown in FIG. 4, the deviation in the distribution ofthe light emission intensity within the light extracting surface isimproved compared to that in Comparative Example 1 (FIG. 7) andComparative Example 2 (FIG. 8). In this case shown in FIG. 4, theforward voltage (Vf) is 3.70V, the optical output (Po) is 586 mW, andthe luminous efficiency (WPE) is 31.7%.

Comparative Example 1

The light emitting element according to Comparative Example 1 includesthe upper electrode having an extending portion with a rectangular ringshape extending in an approximately rectangular shape along the outerperiphery of the semiconductor layer and two linear extending portionsthat divide the region surrounded by the rectangular ring shape in threeequal parts. Further, two pad portions are respectively disposed at twointersections of one of four sides of the rectangular ring shape withthe two linear extending portions.

As shown in FIG. 7, the light emission intensity is higher in theregions at the side where the pad portions are provided and lower inother regions, indicating occurrence of deviation in the distribution ofthe light emission intensity within the light extracting surface. Inthis case shown in FIG. 7, the forward voltage (Vf) is 3.74V, theoptical output (Po) is 579 mW, and the luminous efficiency (WPE) is31.0%.

Comparative Example 2

The light emitting element according to Comparative Example 2 differsfrom that of Comparative Example 1 in that the pad portions are arrangedat two corners at the same side of the rectangular ring shape, which isan approximately the shape of the electrode of conventional lightemitting elements (see JP 2013-197197 A).

As shown in FIG. 8, the light emission intensity is higher in theregions at the side where the pad portions are provided and lower inother regions, indicating occurrence of deviation in the distribution ofthe light emission intensity within the light extracting surface. Inthis case shown in FIG. 8, the forward voltage (Vf) is 3.74V, theoptical output (Po) is 582 mW, and the luminous efficiency (WPE) is31.1%.

The forward voltages (Vf), the optical outputs (Po), and the luminousefficiencies (WPE) of Example 1, Comparative Example 1, and ComparativeExample 2 are shown in Table 1 for the ease of comparison.

TABLE 1 Vf (V) Po (mW) WPE (%) Example 1 3.70 586 31.7 ComparativeExample 1 3.74 579 31.0 Comparative Example 2 3.74 582 31.1

As shown in Table 1, with respect to Comparative Example 1, Example 1shows a 0.04 V lower Vf value, a 7 mW higher Po value, and a 0.7% higherWPE value. Further, with respect to Comparative Example 2, Example 1shows a 0.4 V lower Vf value, a 4 mW higher Po value, and a 0.6% higherWPE value. Thus, any values obtained in Example 1 are higher than thatof Comparative Example 1 and Comparative Example 2.

The light emitting elements according to embodiments of the presentinvention can be used, in addition to for general lighting, for variouslight sources for backlights of liquid crystals, headlights forvehicles, signals, large-scale displays, exposure devices, or the like.It is to be understood that although the present invention has beendescribed with regard to preferred embodiments thereof, various otherembodiments and variants may occur to those skilled in the art, whichare within the scope and spirit of the invention, and such otherembodiments and variants are intended to be covered by the followingclaims.

What is claimed is:
 1. A light emitting element comprising: asemiconductor structure; an upper electrode disposed on an upper surfaceof the semiconductor structure; and a lower electrode disposed on alower surface of the semiconductor structure, wherein, in the plan view,the upper electrode comprises: a first extending portion extending in anapproximately rectangular shape, a first pad portion connected andadjacent to a first side among four sides of the first extendingportion, a second pad portion connected and adjacent to a second sidethat is opposite to the first side among the four sides of the firstextending portion, and a second extending portion and a third extendingportion, each disposed in a region surrounded by the first extendingportion, the second extending portion and the third extending portioneach connecting the first pad portion and the second pad portion,wherein a first straight line connecting the first pad portion and thesecond pad portion divides the region surrounded by the first extendingportion into a region on the side of the third side among the four sidesand a region on the side of the fourth side which is opposite to thethird side, the second extending portion is arranged in a region on theside of the third side and the third extending portion is arranged in aregion on the side of the fourth side.
 2. The light emitting elementaccording to claim 1, wherein on a second straight line perpendicularlybisecting the first straight line, a distance between the secondextending portion and the third extending portion is equal to or greaterthan a shortest distance between the first extending portion and thesecond extending portion, and equal to or greater than a shortestdistance between the first extending portion and the third extendingportion.
 3. The light emitting element according to claim 1, wherein ona second straight line perpendicularly bisecting the first straightline, the shortest distance between the first extending portion and thesecond extending portion is the same as the shortest distance betweenthe first extending portion and the third extending portion.
 4. Thelight emitting element according to claim 1, wherein (i) a ratio of theshortest distance between the first extending portion and the secondextending portion, a distance between the second extending portion andthe third extending portion, and the shortest distance between the firstextending portion and the third extending portion on a second straightline perpendicularly bisecting the first straight line, and (ii) a ratioof a shortest distance between the first extending portion and thesecond extending portion, a distance between the second extendingportion and the third extending portion, and the shortest distancebetween the first extending portion and the third extending portion on adiagonal line of the first extending portion, are substantially thesame.
 5. The light emitting element according to claim 1, wherein thefirst pad portion and the second pad portion are arranged on a thirdstraight line passing through an intersection point of lines extendingdiagonally across the first extending portion.
 6. The light emittingelement according to claim 5, wherein the first straight line isapproximately parallel to the third side and the fourth side.
 7. Thelight emitting element according to claim 6, wherein the secondextending portion includes a portion approximately parallel to the thirdside, and a parallel portion of the second extending portion has alength of at least a half of a length of the third side, and wherein thethird extending portion includes a portion approximately parallel to thefourth side, and a parallel portion of the third extending portion has alength of at least a half of a length of the fourth side.
 8. The lightemitting element according to claim 1, wherein the second extendingportion and the third extending portion are spaced apart from each otherand are each connected to the first pad portion and the second padportion.
 9. The light emitting element according to claim 8, wherein thefirst extending portion, the second extending portion, and the thirdextending portion are connected to the first pad portion and the secondpad portion at equal intervals from adjacent extending portions atintervals of 60 degrees.
 10. The light emitting element according toclaim 1, wherein, on a second straight line perpendicularly bisectingthe first straight line, the distance between the second extendingportion and the third extending portion is greater than the shortestdistance between the first extending portion and the second extendingportion, and greater than the shortest distance between the firstextending portion and the third extending portion.
 11. The lightemitting element according to claim 3, wherein (i) a ratio of theshortest distance between the first extending portion and the secondextending portion, a distance between the second extending portion andthe third extending portion, and the shortest distance between the firstextending portion and the third extending portion on the second straightline, and (ii) a ratio of the shortest distance between the firstextending portion and the second extending portion, a distance betweenthe second extending portion and the third extending portion, and theshortest distance between the first extending portion and the thirdextending portion on a diagonal line of the first extending portion, aresubstantially the same.
 12. The light emitting element according toclaim 1, wherein the first pad portion and the second pad portion areconnected and adjacent to inner sides of the first extending portion.13. The light emitting element according to claim 1, wherein the secondextending portion and the third extending portion are curved.
 14. Thelight emitting element according to claim 5, wherein the first straightline is at an angle to the third side and the fourth side which areamong the four sides of the first extending portion.